A protocol for the radiological assessment for agricultural use of land in Ukraine abandoned after the Chornobyl accident

There is a need in Ukraine for re-evaluation of the status of lands outside the Chornobyl Exclusion Zone which were abandoned in the years after the accident. Since the 1991 criteria for zoning were put in place, there has been no re-classification of abandoned lands even though radionuclide contamination density and, for radiocaesium isotopes, mobility have both declined. This study describes the development of a protocol for assessment of abandoned lands in Ukraine based on a 100 ha experimental plot. A simple method of quantification of ¹³⁷Cs contamination density was developed using external dose measurement whilst other relevant radionuclides (⁹⁰Sr; ²⁴¹Am and Pu isotopes) were quantified using selected soil samples. Modelling of uptake of radionuclides in eight key crops shows that the study field could be re-used for agriculture according to Ukrainian regulatory limits. Monte Carlo modelling of potential dose to farm workers showed that dose was dominated by external exposure and that doses were significantly below 1 mSv y⁻¹. Based on statistical analysis of soil-plant concentrations ratios, criteria were derived for assessment of suitability of agricultural land for production. The criteria are applicable to areas of soddy-podzolic sandy and sandy loam soils (Podzoluvisol) typical in these regions of Northern Ukraine. They are not applicable to high organic matter soils (Histosols) where soil-plant concentration ratios are likely to be much higher for radiocaesium.